Bar code scanner and method of scanning

ABSTRACT

A method and an apparatus facilitate scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon by sweeping a scanning beam in a scan path across the Add-On code portion of the label. The bar code label includes bar codes of the type which have a primary code portion and which may also have an Add-On code portion. The method includes the steps of: optically scanning the label and producing an electrical signal indicative of the image of the label which includes a possible Add-On code portion; providing data indicative of the structure of the possible Add-On code portion in response to the electrical signal; subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an adjacent margin; subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an Add-On guard pattern; decoding the characters of the possible Add-On code portion of the label; and terminating decoding.

This is a continuation of application Ser. No. 07/922,875 filed Jul. 31, 1992, now U.S. Pat. No. 5,311,000

BACKGROUND OF THE INVENTION

The present invention relates to a computer controlled, bar code scanner apparatus and a method of scanning and, more particularly, to such scanning apparatus and to such a method in which bar code labels of the type including supplemental encodations, termed "Add-On" code portions or segments, are rapidly and reliably scanned without the need for operator adjustment of the scanner apparatus.

Bar code labels are used on a broad range of retail packages and products for check-out and inventory purposes. A scanner, located for example at the check-out station in a retail establishment, is used by a clerk to enter product identification data into an associated computer system.

Typically, a scanner of this type includes a laser source, such as a gas discharge laser or a laser diode, which produces a low power laser beam. The beam passes through appropriate optical lenses and is swept across the package surface by a motor-driven, rotating mirror assembly. In some scanners, the package bearing a bar code label is presented manually to the stationary scanner by a clerk. In other scanners, the scanner is designed to be held by the clerk, and aimed generally at the package. In either event, a portion of the light reflected from the package surface returns through the optical lenses to a detector which provides an electrical signal in dependence upon the level of the reflected light. A signal processing system then analyses the electrical signal produced as the beam sweeps over the bar code label, decoding the encoded scan data.

The scan data may then be transmitted to a host computer or terminal, which determines the total price of the products being purchased, as well as storing the identity of the purchased products for inventory and accounting purposes. The host computer or terminal may be dedicated to a single scanner. Alternatively, a single host computer or terminal may service a number of scanners at the retail establishment.

A number of different bar codes have come into use. The more common ones are generally horizontal in design with alternating vertical dark bars and light spaces therebetween. Groupings of dark bars and light spaces make up the bar code characters. The height of the bars has no purpose other than to permit a scanning beam to successfully pass over the entire length of at least one of the bar code portions or segments to permit reading the portion or segment in one scanning pass. A segment is a set of characters that forms a portion of a valid label. A UPC-A label contains two segments, a left UPC-A segment containing six characters and a right UPC-A segment containing six characters. An EAN 13 label contains two segments, a left EAN 13 segment, containing six characters and a right EAN 13 segment containing six characters. An EAN 8 label contains two segments, a left EAN 8 segment containing four characters and a right EAN 8 segment containing four characters. A UPC-E label contains one segment having six characters. Common codes include Code Three of Nine, Two of Five, Codabar, Two of Five Non-Interleaved, Two of Five Interleaved, UPC-A, UPC-E, EAN 13, and EAN 8.

The boundaries of segments are distinct bar and space patterns referred to as "guard," "margin," and "center-band" patterns. The guard or margin pattern is the start pattern and the center-band pattern is the stop pattern of a left half segment. The center-band pattern is the start pattern and the guard or margin pattern is the stop pattern of a right half segment.

Also in use is a two or five character "Add-On" supplemental code portion for UPC and EAN labels. An Add-On supplemental code portion is simply an additional grouping of bars and spaces, to one side of the primary bar code portion, which includes additional data to be read by the scanner. The Add-On contains only one bounding pattern, an Add-On guard pattern on the side of the Add-On portion adjacent to the main label. The side of the Add-On portion facing away from the main label portion is unbounded. Add-On code portions are supplemental encodations which were designed principally for use on periodicals and paperback books. Generally, nothing in the main portion of the label indicates whether a Add-On portion is included in the label.

Used in conjunction with the UPC symbol, they satisfy a number of requirements. For UPC-A, EAN 8, EAN 13 and UPC-E symbols, the first bar of the supplemental encodation symbol is separated by a margin, which is nominally nine modules, from the last bar of the UPC symbol. The supplemental encodations are unlikely to be confused with UPC symbols for any existing scanner designs. The decode algorithm for the supplemental Add-On encodations is similar to that for the UPC code. The two character supplemental code was designed for periodical issue number.

Although compatible with the UPC symbol, an Add-On code portion is not mistaken for UPC symbols by scanners designed to read only standard UPC symbols because the Add-On code portion includes information indicating the presence of an Add-On code portion such as a unique guard pattern, and each character of the Add-On code portion is separated from the next character by a delineator character which is encoded 01 (each digit represents a module; "0" represents a light or white space of one module width and "1" represents a dark module or bar of one module width). The left-hand guard pattern for a supplemental Add-On portion is unique, encoded as 1011, differentiating it from the left-hand and right-hand guard bar patterns of the UPC which are encoded 101. A right-hand pattern for the Add-On code portion is not used.

A primary requirement for high volume transaction laser scanners is to operate in a way that the store check-out clerk does not have to worry about the label orientation as the product label is passed over the scanner. The basic function of the scan pattern generating arrangement associated with a scanner is to move the beam of laser light repetitively through a three dimensional pattern. In this way, the scanner is capable of finding and reading labels in as many label orientations as possible.

Since previously it was desired, and in some scanner systems required, that the scanning beam sweep across all of the portions of the label in a single pass, bar code labels including an Add-On code portion present a particularly difficult problem. Such labels have a high aspect ratio, i.e., the ratio of their horizontal dimension to their vertical dimension is particularly large. As a consequence, the range of the orientation of the scan path of the scanning beam of light which has produced a successful read of such labels in prior art systems is more limited than is the case with labels which do not include an Add-On code portion. If a primary code area were read by a conventional scanner and no Add-On code portion were read during the same scanning pass, this might have resulted from the particular orientation of the bar code label with respect to the scan path. Alternatively, this may have resulted from reading a bar code label which did not include an Add-On code portion.

Previously, the approach has been for the clerk operating a scanner to switch the scanner to a special setting when labels having an Add-On code portion were to be read. In this setting, the scanner would acknowledge a valid "read" only when one or two segments of the primary code portion and the Add-On supplemental code portion of a label were both read in the same scanning pass of the beam. When switched to the normal scanner setting, the scanner would read the primary code portion and ignore the Add-On code portion as superfluous.

As will be appreciated, switching the scanner back and forth is time consuming and burdensome. Further, the possibility exists for an erroneous reading of a label in the event that the scanner is switched to the wrong setting.

In other prior systems, it has been required that an Add-On code portion be scanned in the same scanning pass as at least one segment of the primary code portion of the label. As a result, the operation of the scanner was slowed somewhat, and the likelihood of a successful reading of a label reduced.

Accordingly, there is a need for a scanner and a method of scanning in which bar code labels may be read automatically, whether or not they include an Add-On code portion, and in which an Add-On code portion can be quickly recognized and read without simultaneously reading the primary code portion of the label.

SUMMARY OF THE INVENTION

This need is met by a method and an apparatus according to the present invention for scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon. A scanning beam is swept in a scan path across the Add-On code portion of the label. The bar code labels bear bar codes of the type which include a primary code portion and which may also include an Add-On code portion. The method includes the steps of: optically scanning the label and producing an electrical signal indicative of the image of the label which includes a possible Add-On code portion, as by sweeping a scanning beam across the label until the beam sweeps a scanning pass along a scan path which traverses a possible Add-On code portion; providing data indicative of the structure of the possible Add-On code portion in response to the electrical signal; subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an adjacent margin; subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of information comprising an Add-On guard pattern; decoding the characters of the possible Add-On code portion of the label; and terminating decoding. It will be appreciated that the order in which these steps are performed is not critical, and it is within scope of the present invention to perform these steps in various orders, or to perform two or more of these steps simultaneously.

The step of subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an Add-On guard pattern may comprise the step of checking to determine whether:

Margin<5*(G1+G2+G3), and

Margin>(G1+G2+G3), and

3/2>G1/G2>2/3, and

5/2>G3/G1>3/2,

where G1 is the width of the first bar element of the guard pattern of the possible Add-On code portion, G3 is the width of the second bar element of the guard pattern of the possible Add-On code portion, and G2 is the width of the space between the first and second bar elements of the guard pattern of the possible Add-On code portion. The tests do not have to use the exact limits specified above.

The step of subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an adjacent margin comprises the step of checking to determine whether a margin exists adjacent to the Add-On guard pattern of the possible Add-On code portion which is greater than a predetermined minimum width and less than a predetermined maximum width.

The predetermined minimum width may be approximately 4 modules in width and the predetermined maximum width may be approximately 20 modules in width, the guard pattern of the possible Add-On code portion consisting of a one module width, first bar element, a two module width, second bar element, and a one module space between the first and second bar elements.

The step of decoding the characters of the Add-On code portion of the label includes the steps of: decoding the first possible character of the possible Add-On code portion, and checking for the existence of an adjacent intercharacter delineator consisting of a bar of width S1 and a space of width S2, decoding each successive possible character after checking for the existence of a preceding intercharacter delineator consisting of a bar of width S1 and a space of width S2, except for the last character in an Add-On code portion since such a character has no following delineator.

The widths of the bar and the space making up each intercharacter delineator are checked to determine that

S2<2*m and

S1<2*m

where m is the nominal single module width calculated from the preceding character,

failing which the possible Add-On Code portion is determined not to be an Add-On code portion of a label, and decoding is terminated. For UPC and EAN codes, the nominal single module width is calculated by dividing the preceding character width by seven, since the code rules require a character to be seven modules in width.

The step of decoding each successive possible character after checking for the existence of a preceding intercharacter delineator, consisting of a bar of width S1 and a space of width S2, continues until the first of the following occurs: a) five characters are decoded; b) a character cannot be decoded; or c) an intercharacter delineator does not precede the last character decoded and a trailing margin or white space is found.

Apparatus according to the present invention scans an Add-On code portion of a bar code label to determine the bar code data printed thereon. The bar code label includes a primary code portion and an Add-On code portion. The apparatus includes means for optically scanning the label and producing an electrical signal indicative of the image of the label which includes a possible Add-On code portion. The apparatus further includes means, responsive to the electrical signal, for providing data indicative of the structure of the possible Add-On code portion. The apparatus further includes a means for subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an adjacent margin, and a means for subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an Add-On guard pattern. Finally, the apparatus includes means for decoding the characters of the possible Add-On code portion of the label; and means for terminating decoding.

The means for subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an Add-On guard pattern comprises means for checking to determine whether:

Margin<5*(G1+G2+G3), and

Margin>(G1+G2+G3), and

3/2>G1/G2>2/3, and

5/2>G3/G1>3/2,

where G1 is the width of the first bar element of the guard pattern of the possible Add-On code portion, G3 is the width of the second bar element of the guard pattern of the possible Add-On code portion, and G2 is the width of the space between the first and second bar elements of the guard pattern of the possible Add-On code portion. The tests do not have to use the exact limits specified above.

The means for subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an adjacent margin comprises means for checking to determine whether a margin exists adjacent to the Add-On guard pattern of the possible Add-On code portion which is greater than a predetermined minimum width and less than a predetermined maximum width.

The predetermined minimum width may be approximately 4 modules in width and the predetermined maximum width may be approximately 20 modules in width. The guard pattern of the possible Add-On code portion consists of a one module width, first bar element, a two module width, second bar element, with a one module space between the first and second bar elements.

The means for decoding the characters of the Add-On code portion of the label includes: means for decoding the first possible character of the possible Add-On code portion, means for checking for the existence of an adjacent intercharacter delineator consisting of a bar of width S1 and a space of width S2, and means for decoding each successive possible character after checking for the existence of a preceding intercharacter delineator consisting of a bar of width S1 and a space of width S2.

The widths of the bar and the space making up each intercharacter delineator are checked to determine that

S2<2*m and

S1<2*m

where m is the nominal single module width calculated from the preceding character,

failing which the possible Add-On code portion is determined not to be an Add-On code portion of a label, and decoding is terminated. For UPC and EAN codes, the nominal single module width is calculated by dividing the preceding character width by seven, since the code rules require a character to be seven modules in width.

The means for decoding each successive possible character after checking for the existence of a preceding intercharacter delineator consisting of a bar of width S1 and a space of width S1, includes means for continuing until the first of the following occurs: a) five characters are decoded; b) a character cannot be decoded; or c) an intercharacter delineator does not precede the last character decoded. The apparatus may further include means for locating a trailing margin having a predetermined minimum width after five characters are decoded.

Accordingly, it is an object of the present invention to provide a method and an apparatus for scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon in which the successful location and decoding of an Add-On code portion is not dependent upon the successful location and decoding of any portion of the bar code label or segments thereof; and to provide such a method and apparatus in which the Add-On code portion of a label may be quickly, simply decoded.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a sales clerk at a check-out counter, using a laser scanner to scan a bar code label;

FIG. 2 is a perspective view of the laser scanner and a package disposed above the scanner and parallel to the front edge thereof and in a vertical position wherein a cross bar X scan pattern is projected on the scanner window and on the package face;

FIGS. 3-5 are perspective views similar to that of FIG. 2 but showing the cross bar X scan pattern on a package disposed at different orientations with respect to the laser scanner;

FIG. 6A is a pictorial representation of a UPC-A bar code label, including a primary code portion and a two character Add-On code portion;

FIG. 6B is a pictorial representation of a UPC-A bar code label, including a primary code portion and a five character Add-On code portion;

FIG. 6C is a pictorial representation of an EAN 13 bar code label, including a primary code portion and a two character Add-On code portion;

FIG. 6D is a pictorial representation of an EAN 13 bar code label, including a primary code portion and a five character Add-On code portion;

FIG. 6E is a pictorial representation of an EAN 8 bar code label, including a primary code portion and a two character Add-On code portion;

FIG. 6F is a pictorial representation of an EAN 8 bar code label, including a primary code portion and a five character Add-On code portion;

FIG. 7 is a pictorial representation of a Two of Five Non-Interleaved bar code, including a primary code portion and an Add-On code portion; and

FIG. 8A is a pictorial representation of a one-segment UPC-E bar code, including a primary code portion and a two character Add-On code portion;

FIG. 8B is a pictorial representation of a one-segment UPC-E bar code, including a primary code portion and a five character Add-On code portion; and

FIG. 9 is a flow chart depicting steps which are used to determine the existence of an Add-On guard pattern.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 of the drawings illustrates a computer controlled bar code scanner according to the present invention for scanning bar code labels to determine the bar code data printed thereon. As is explained more fully below, this bar code scanner is capable of scanning bar code labels having scan data printed thereon in bar codes of the type which include a primary code portion and which may also include an Add-On code portion. FIG. 1 is a pictorial view of a sales clerk C at a check-out counter, with a laser scanner system of this type being used to scan a product label.

The clerk C manually passes the product across a scanning station over a window W. The scanning beam emerges from the window so as to permit the beam to be swept across the label. A portion of the light reflected from the label passes downward from the arrangement of bars on the product label. The beam is caused to rapidly sweep through a series of scan paths which collectively produce a scan pattern in which the likelihood of a successful scan is high. It is desired that the scan pattern be such that it is highly probable that at least one scan path will traverse the label in a direction more or less perpendicular to the bars making up the bar code.

The scanner system of the present invention includes a scanner S comprising a scanner means for sweeping a scanning beam across the scanning station and providing an electrical scan signal indicating markings on surfaces presented to the scan station. The scanner also includes computer means, such as a microprocessor M, which is responsive to the scan signal for interpreting the scan signal as scan data signified by the scanned bar code labels. The computer means M determines whether a bar code label has been scanned properly, and whether valid scan data has been obtained, and supplies the scan data to the associated host computer COM.

In common with many scanners in use today, the illustrated scanner uses a variation of what is called a "cross-bar X" scan pattern. FIG. 2 illustrates this scan pattern on the window W of the scanner S and on a face F of a package P, bearing a bar code label L, disposed parallel to the front edge E of the scanner S and in a vertical position. The cross bar X pattern consists of five scan lines: the center horizontal (CH) line, right and left side horizontal (RSH & LSH) lines, and right and left vertical (RV & LV) lines. Note the orthogonality of the RV and LV scan lines with the CH scan lines. Also note that in this instance, the CH scan line passes over the bar code label in a direction which is generally perpendicular to the bars making up the code.

A more intuitive understanding of this scan pattern can be gained by examining depictions of the scan pattern on the package P in different orientations, as shown in FIGS. 3-5. In FIG. 3, the package face F is disposed parallel to the front edge E of the scanner S but leaned forty-five degrees toward the top T of the scanner. Note the orthogonality of the RV and RSH scan lines. In FIG. 4, the package face F is disposed in a vertical position but rotated forty-five degrees from the front edge E of the scanner S. Note the orthogonality of the LV and LSH scan lines. In FIG. 5, the package face F is rotated forty-five degrees from the front edge E of the scanner S and leaned forty-five degrees toward the top T of the scanner. Note the orthogonality of the LV and CH scan lines. In each of FIGS. 2-5, there is at least one set of perpendicularly crossing scan lines even though the label planes are at very different locations. Also note that scan lines CH and LSH are properly positioned for scanning the label L in FIGS. 2 and 5, respectively, that a scan line does not cross the label L in FIG. 4, and that scan lines LV and CH only pass over a portion of the bar code in FIG. 3.

Among the UPC and EAN bar codes, UPC-A, UPC-E, EAN 13 and EAN 8 labels support supplemental two and five character Add-On code portions. These supplemental codes are optionally appended to the standard labels. Previously, Add-On code portions have been scanned and read less reliably than the standard codes. There are two reasons for this: (1) less effective error checking capabilities are used, especially in the case of two character Add-On code portions, and (2) the standard label may be read without the Add-On code portion and usually no flag is used in the primary code portion to indicate that an Add-On code portion is being used.

Reference is now made to FIGS. 6, 7, and 8 which depict several different bar codes. FIG. 6A shows a UPC-A bar code having a primary code portion 10 and a two character Add-On code portion 12. Most UPC bar codes are two segment codes. That is, the primary code portion 10 is made up of an A segment, and a B segment. Typically, conventional scanners have permitted the two segments to be read during different scanning passes in order to increase the range of label orientations in which successful scanning may be accomplished. FIG. 6B shows a UPC-A bar code having a five character Add-On code portion. FIG. 6C shows an EAN 13 bar code having a two character Add-On portion. 6D shows an EAN 13 bar code having a five character Add-On portion. 6E shows an EAN 8 bar code having a five character Add-On portion. 6F shows an EAN 8 bar code having a five character Add-On portion.

Similarly, FIG. 7 shows a Two of Five Non-Interleaved bar code having a primary code portion 10 and an Add-On code portion 12. FIG. 8A shows a UPC-E bar code having a primary code portion 10 and a two character Add-On code portion 12. Both of these codes are single segment codes. The Two of Five Non-Interleaved bar code is not presently in significant commercial use in the United States. FIG. 8B shows a UPC-E bar code having a primary code portion and a five character Add-On code portion.

As discussed above, it has not been simple previously for a scanner to scan both bar code labels having Add-On code segments and bar code labels not having Add-On code segments without the operator differentiating between the two types of bar code labels and providing to the scanner an indication of which type is currently being scanned. This has been true due to the geometry of the codes. Referring to FIG. 7, for instance, it will be seen that any number of successful scans of the primary code portion 10 may be made along a scan line between outer lines 14 and inner lines 16 without the scan line crossing the Add-On code portion 12. As a consequence, an ambiguity existed which was resolved by operator intervention in the scanner operation. This ambiguity was even greater with typical two-segment UPC codes, as illustrated by the spread between outer scan lines 18 and inner scan lines 20 in FIG. 6A. Finally, the greatest ambiguity is found with respect to UPC-E bar codes, as illustrated by the spread between outer scan lines 22 and inner scan lines 24 in FIG. 8A. This level of ambiguity is equaled in bar code scanners which permit either segment to be scanned alone during a single scanning pass.

One approach to scanning labels with Add-On segments and labels without Add-On segments without the need for operator intervention involved redundant scanning passes. More than one scanning pass of a label without scanning an Add-On segment was required to determine if an Add-On segment was present. Furthermore, scanning of an Add-On segment required simultaneous scanning of the adjacent segment of the primary code portion of the label. It will be appreciated that these requirements significantly slowed the scanning operation.

The present invention overcomes these difficulties by effecting scanning and decoding of an Add-On code portion as a completely separate operation, unrelated to the scanning of the primary code portion of the bar code label. The algorithm for finding a separate supplemental Add-On code segment relies on the structure of Add-On code portions specified in the UPC Symbol Specification Manual, January 1986 version by the Uniform Code Council, Inc., and the "General EAN Specification" 1987 version by the International Article Numbering Association. These documents specify requirements for the supplemental Add-On symbology. In the construction of the Add-On decoding algorithm, these specifications are relied upon for the leading and trailing margins, intercharacter delineators, the Add-On guard band, and the previous segment.

In the method of the present invention, an Add-On code portion of a bar code label to determine the bar code data printed thereon may be scanned by sweeping a scanning beam in a scan path across the Add-On code portion of the label. It will be appreciated, however, that other scanning techniques may be utilized to perform the scanning function. If desired, for example, the surface bearing the bar code segments may be imaged by video imaging techniques, and scan data taken from the pixel information acquired in this manner.

For purposes of illustration, however, a scanning beam may be swept across the label until the beam sweeps a scanning pass along a scan path which traverses a possible Add-On code portion. The scanner then provides data indicative of the structure of the possible Add-On code portion. This data is subjected to at least one test to determine the existence of an adjacent margin. Preferably, this is accomplished by checking to determine whether a margin exists adjacent to the Add-On guard pattern of the possible Add-On code portion which is greater than a predetermined minimum width and less than a predetermined maximum width. The predetermined minimum width is approximately 4 modules in width and the predetermined maximum width is approximately 20 modules in width. The above referenced specifications call for a margin between 7 and 12 modules in width. As a result, the relaxed limits used in this method allow the system to read segments that do not meet the uniform specifications due to printing errors. If these tests are not met, the decoding operation is terminated for this possible Add-On code portion.

Next, assuming that a margin of acceptable dimensions is found, the data indicative of the structure of the possible Add-On code portion is subjected to at least one test to determine the existence of an Add-On guard pattern. The Add-On guard pattern is checked for the distinctive pattern of a single module wide bar and a single module wide space followed by a two module wide bar, see for example the Add-On guard pattern 30 shown in FIG. 6B. This is done by the following tests, which are shown in the flow chart of FIG. 9 where G1 is the first bar element and G3 is the second bar element, with G2 being the separating space:

Margin<5*(G1+G2+G3), and

Margin>(G1+G2+G3), and

3/2>G1/G2>2/3, and

5/2>G3/G1>3/2,

If these tests are not met, the decoding operation is terminated for this possible Add-On code portion. If these tests are met, however, the first character of the Add-On code portion is then decoded. The character specifications remain unchanged from that used for the main label characters. As a consequence, a conventional decoding algorithm is used for the actual character decoding operation. The total number of characters in a standard Add-On code segment is either two or five.

Following each character, except the last one of an Add-On code portion, is an intercharacter delineator or delineator character consisting of a single module wide bar S1 and a single module wide space S2. The present invention determines the existence of a valid intercharacter delineator after decoding each character by implementing the following tests:

S2<2*m and

S1<2*m

where m is the nominal single module width calculated from the preceding character. Each character of a UPC code is, by definition, seven modules in width. As a consequence, the width of the preceding character is divided by seven to calculate a nominal value for the width of a module. If either of the above two tests fails, the Add-On code portion is rejected.

The step of decoding each successive possible character after checking for the existence of a preceding intercharacter delineator consisting of a bar of width S1 and a space of width S2 continues until the first of the following occurs:

a) five characters are decoded;

b) a character cannot be decoded; or

c) an intercharacter delineator does not precede the last character decoded.

Finally, after the first of the above occurs, a check is made to determine the existence of a trailing margin having a predetermined minimum width. This trailing margin must be at least five modules wide. There is no upper limit to the size of the trailing margin. If this test fails, the Add-On code portion is rejected. This test reduces the chances of scanning a portion of a five character Add-On and decoding it as a two character Add-On.

The method of the present invention is carried out by means of a scanner of conventional design operating in conjunction with a programmed microprocessor. An appropriate source code listing for effecting this method follows. ##SPC1##

Having described the invention in detail and by reference to the preferred embodiments thereof, it will be apparent that other modifications and variations are possible without departing from the scope of the invention defined in the appended claims. 

What is claimed is:
 1. A method of scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon by sweeping a scanning beam in a scan path across the bar code label, said bar code label bearing a bar code of the type which includes a primary code portion and which may also include an Add-On code portion, said method comprising the steps of:sweeping a scanning beam across the label until the beam sweeps a scanning pass along a scan path which traverses a possible Add-On code portion; providing data indicative of the structure of the possible Add-On code portion; subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an adjacent margin; subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of information indicating the presence of an Add-On code portion without requiring the successful location of any portion of the primary code portion; decoding the characters of the Add-On code portion of the label without requiring the successful decoding of any portion of the primary code portion; and terminating decoding.
 2. The method of scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon according to claim 1, in which the step of subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of information indicating the presence of an Add-On code portion comprises the step of subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an Add-On guard pattern.
 3. The method of scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon according to claim 2, in which the step of subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an Add-On guard pattern comprises the step of checking to determine whether:Margin<5*(G1+G2+G3), and Margin>(G1+G2+G3), and 3/2>G1/G2>2/3, and 5/2>G3/G1>3/2,where G1 is the width of the first bar element of the guard pattern of the possible Add-On code portion, G3 is the width of the second bar element of the guard pattern of the possible Add-On code portion, and G2 is the width of the space between the first and second bar elements of the guard pattern of the possible Add-On code portion.
 4. The method of scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon according to claim 1, in which the step of subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an adjacent margin comprises the step of checking to determine whether a margin exists adjacent to the possible Add-On code portion which is greater than a predetermined minimum width and less than a predetermined maximum width.
 5. The method of scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon according to claim 4, in which said predetermined minimum width is approximately 4 modules in width and the predetermined maximum width is approximately 20 modules in width.
 6. A method of scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon by sweeping a scanning beam in a scan path across the bar code label, said bar code label bearing a bar code of the type which includes a primary code portion and which may also include an Add-On code portion, comprising the steps of:sweeping a scanning beam across the label until the beam sweeps a scanning pass along a scan path which traverses a possible Add-On code portion; providing data indicative of the structure of the possible Add-On code portion; subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of information indicating the presence of an Add-On code portion without requiring the successful location of any portion of the primary code portion; decoding the characters of the Add-On code portion of the label without requiring the successful decoding of any portion of the primary code portion; and terminating decoding.
 7. Apparatus for scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon, said bar code label bearing a bar code of the type which includes a primary code portion and which may also include an Add-On code portion, comprising:means for optically scanning the label and producing an electrical signal indicative of the image of the label which includes a possible Add-On code portion; means, responsive to said electrical signal, for providing data indicative of the structure of the possible Add-On code portion; means for subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an adjacent margin; means for subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of information indicating the presence of an Add-On code portion without requiring the successful location of any portion of the primary code portion; means for decoding the characters of the Add-On code portion of the label without requiring the successful decoding of any portion of the primary code portion; and means for terminating decoding.
 8. Apparatus for scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon according to claim 7, in which said means for subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of information indicating the presence of an Add-On code portion comprises means for subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an Add-On guard pattern.
 9. Apparatus for scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon according to claim 8, in which said means for subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an Add-On guard pattern comprises means for checking to determine whether:Margin<5*(G1+G2+G3), and Margin>(G1+G2+G3), and 3/2>G1/G2>2/3, and 5/2>G3/G1>3/2,where G1 is the width of the first bar element of the guard pattern of the possible Add-On code portion, G3 is the width of the second bar element of the guard pattern of the possible Add-On code portion, and G2 is the width of the space between the first and second bar elements of the guard pattern of the possible Add-On code portion.
 10. Apparatus for scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon according to claim 7, in which said means for subjecting the data indicative of the structure of the possible Add-On code portion to at least one test to determine the existence of an adjacent margin comprises means for checking to determine whether a margin exists adjacent to the possible Add-On code portion which is greater than a predetermined minimum width and less than a predetermined maximum width.
 11. Apparatus for scanning an Add-On code portion of a bar code label to determine the bar code data printed thereon according to claim 10, in which said predetermined minimum width is approximately 4 modules in width and the predetermined maximum width is approximately 20 modules in width. 